The overall objective of this proposal research is to examine the effect of calcium on renal tubular transport of bicarbonate and fluid and to define the role of calcium in the neural control of these transport processes. Although considerable studies have established that Ca is a mediator between stimulus and response in a variety of cells, little attention has been given to the role of Ca in renal tubular transport. Using tubular and peritubular capillary microperfusion method, I wish to examine the effects of alterations of extracellular and intracellular [Ca] on the proximal tubular absorption of bicarbonate and fluid in rat kidney. Bicarbonate will be determined by microcalorimetric method. The tubular permeability to bicarbonate and sucrose will be also measured. Ca ionophore, Ca channel blockers and Ca-chelating agents will be used to maneuver intracellular [Ca]. Moreover, experiments will be carried out to test the hypothesis that Ca mediates the effects of neurotransmitters on proximal tubular transport. Information obtained from this study will further contribute to our knowledge on neural control of renal function and cellular regulation of transport processes.